It is known in the prior art to provide a power control pedal and a brake control pedal for the operator of a trolley vehicle, such that the operator can determine the acceleration rate of the vehicle by selecting the amount of movement that he provides to the power pedal. The propulsion motor control responds to this movement of the power pedal to provide a vehicle acceleration rate in accordance with a constant current. For example, this constant current can correspond with an acceleration rate of three miles per hour per second, and the motor current remains at that constant current as the vehicle speed increases until the motor curve is reached. Then the motor current decreases as the motor speed increases in accordance with the motor curve up to some maximum motor speed where there is a balance provided between the train movement resistance and the output speed of the propulsion motors. The operator controlled position of the power pedal establishes the acceleration rate of the vehicle before the motor curve is reached.
The required tractive effort to accelerate the vehicle is determined in relation to the vehicle weight, the number of propulsion motors per vehicle, and the effective train resistance, and then a desired value of motor current is established in relation to this required tractive effort. The well-known motor curve relationship is utilized to determine how long will be required for the vehicle to reach a desired speed in relation to a given value of motor current.
It is known in the prior art as taught by U.S. Pat. No. 4,095,153 to provide a chopper control apparatus for a propulsion motor, which apparatus has a phase angle controller that builds up the actual motor current in response to a requested value of motor current by adjusting the ON/OFF duty cycle of the chopper as necessary to maintain this requested current. As the motor speed increases, this requires move average motor volts and the chopper phase angle is increased to reach the value of motor current and to maintain that value of motor current when the chopper is full ON. The chopper then provides full line voltage across the motor when full ON, with the current falling off as the motor operation follows the motor curve up to the maximum vehicle speed where the provided tractive effort balances the train movement resistance for the particular vehicle load.
The operator power pedal position provides a rate request which translates into required tractive effort and requested motor current. The chopper apparatus phase angle provides that requested motor current until the chopper is full ON and then the current decreases as the motor operation follows the motor curve for the propulsion motor.